This invention relates to generally to the formation of a bit line over capacitor array of memory cells.
This invention was principally motivated in addressing problems and improvements in dynamic random access memory (DRAM). As DRAM increases in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. One principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors. Yet as feature size continues to become smaller and smaller, development of improved materials for cell dielectrics, as well as the cell structure, are important.
Conventional stacked capacitor DRAM arrays utilize either a Capacitor Over Bit line (COB) or a Capacitor Under Bit line (CUB) construction. With a Capacitor Over Bit line construction, the bit line is provided in close vertical proximity to the bit line contact of the memory cell field effect transistor (FET), with the cell capacitors being formed over the top of the word line and bit line. With a Capacitor Under Bit line construction, a deep vertical bit line contact is made through a thick insulating layer to the source/drain region of the cell FET access transistor, with the capacitor construction being provided over the word line and under the bit line.
The present invention relates to a method of reducing electrical shorts between the bit contact and the capacitor cell plate in a Capacitor Under Bit line cell.
The process of the present invention provides a method to prevent a short circuit between a capacitor cell plate and a conductive contact. The present invention provides for a capacitor structure having lower and upper conductive cell plates. The conductive cell plates are separated by a dielectric, and the conductive cell plates and the dielectric have exposed edges. A layer of TEOS is disposed upon the wafer and about the capacitor structure. The TEOS layer encases the exposed edges of the conductive cell plates. A conductive contact structure is then provided adjacent the capacitor structure. The TEOS layer separates the capacitor structure and the conductive contact structure, thereby preventing the conductive structures from shorting together.